Automatic choke valve for carburetors



Dec. 31, 1957 E. w. EICKMEI'ER El'AL 2,818,239

AUTOMATIC CHOKE VALVE FOR CARBURETORS Filed April 3, 1956 INi ENTORSElmer Olson By Edward W E lckme/ef lie/r Attorney AUTOMATIC CHOKE VALVEFORCARBURETORS Edward Wiliiarn Eichmeier, Pontiac, Mich., and ElmerOlson, Rochester, N. Y., assignors to General Motors Corporation,Detroit, Mich., a corporation ot'Deiaware ApplicationApril 3,1956,.Serial No. 575,759.

2 Claims. (Cl. 261-39) This invention relates to carburetors forinternal combustion engines, and, most particularly, to mechanism forautomaticallycontrolling the operations of the choke valve thereof whichregulates the admission of air to'the mixture passages of a carburetor.

It has-been the general practice for a number of years to provide achoke valve for controlling the admissionof air to the carburetor whichcould be moved to closed or partially closed position to variablyrestrict the admission of air to the carburetor in order to provide aricher than normal'mixture of fuel and air for starting purposes. Whenthe engine has started and is operating under its oWn power, it isnecessary to progressively open the choke valve as the enginetemperature increases to gradually decrease the-fuel content of themixture until, when normal temperature is reached, the choke valve iswide open and imposes no restriction on'the air inlet.

These choke valves were originally manually operated and were'positionedwholly by the operator of the vehicle. For a good many years, however,it has been customary to provide in most carburetors in commercial usechoke valves which are automatically controlled in response tovariations in engine-temperature and engine suction, such valves beingheld closed when the'temperature is low, to facilitate starting andbeing gradually opened by the effect of suction as the temperatureincreases after the engine becomes self-operative, until the valves arefully. open when normal operating temperature is reached. Generally, thechoke valve is held closed by a bimetallic thermostat one end of whichis fixed while the other end engages an arm on the choke valve shaft.Opening of the valve is generally effected by a suction operated pistonsubject to variations in suction posterior to the throttle andconnected'to the valve shaft so as toexert a force in opposition to thatof the thermostat, and the valves are also generally unbalanced so as tobe responsive to variations in suction effective directly on the valvesthemselves.

Obviously, an increase in temperature will decrease the force-holding:thevalve:closed, while an increase in suction will increase theforce tending to open the valve so that, after the engine isself-operative, the valve will be moved toward open position by theeffect of suction as the engine temperature increases and also if thesuction is increased without change in temperature. For example, whenthe engine starts ,to,-run under its own power, there is noimmediate-increase intemperature, but there is-a.

I due to.the.redu,ction inthe closing force exerted by the thermostat asthe engine temperatureincreases.

To, effectheating of the thermostanhot air is generally drawn from astove'adjacent the exhaust manifold of the engine throughahousing inwhich the thermostat is p ositionedor'the thermostatis placedinsuch aposition that it is subject to direct radiation from the exhaustmanifold 1' nited States Patent 0 so that the temperature variation ofthe thermostat follows closely the temperature variation of the exhaustmanifold. The intake passage of the intake manifold through whichmixture is conveyed to the engine also generally receives heat from theexhaust manifold and in some engine installations the intake passagereceives so little heat from the exhaust manifold that the increase intemperature of the intake passage is far less rapid than the increase intemperature of the air adjacent the thermostat. In such installations,the choke valve will open too rapidly when the engine first starts torun and the mixture supplied to the engine will be too lean. After thevalve is moved to a predetermined open position and the enginetemperature has considerably increased, the

suction efiective on the piston is reduced so that after the valvereaches such position the difficulty referred to is not encountered.

It is the primary purpose of the present invention-to eliminate thedifficulty above referred to and to provide an automatic choke mechanismhaving a choke valve controlled in accordance with variations in enginetemperature and suction which is provided with means for restricting theapplication of heat to the thermally re sponsive means during a part ofthe movement of the choke valve toward open position, butwhich isrendered ineifective after the choke valve makes a predeterminedmovement toward open position.

It'is'also an object of the invention-to provide in an automatic chokemechanism for a carburetor, having a choke valve movable in response tovariations in engine stat, with a valve operable by the thermostat whichis elfective to close the direct passage and open.the.by-

' pass at relatively low temperatures, but will close the .by-

pass and open the direct passage after. a predetermined termperature isreached.

Further objects and advantages of the present invention will be apparentfrom the following description, reference beiug had to the accompanyingdrawings, wherein a preferred form of the present invention is clearlyshown.

In the drawings:

Figure 1 is a fragmentary elevation, partly in section, showing a partof a carburetor equipped with an automatic choke mechanism in which thepresent invention is incorporated;

Figures 2 and 3 are vertical sectionson the lines 2-2 and 33 of Figure1, respectively, While Fig. 4 is an enlarged detail of a part of Fig. 1.

Since the invention to which this application relates is concernedsolely with the automatic choke mechanism and the specific constructionof the carburetor is. in no sense material, the entire carburetor is.not shown, Fig. 1 showing only the upper,or air intakeend of adown-draft carburetor and the automatic choke mechi anism whichconstitutes the present invention. The carburetor may be of any suitableconstruction such as'that 'shown in the patent to Olson, 2,339,907, May26, 1953, for example, and its structure need not be described herein.

As shown in Fig. .1, the reference numeral .2 indicates-a casting'inwhich is formed a constant level fuel chamber of conventional form whichsupplies fuel to a mixture the lateral extension '56 of the arm 44extends, so that when the thermostat'or the suction operated pistonmoves arm 44, the two arms 98 and 100 are also moved.

Projecting to the .left ofthe lower end of Larm 98 as seen in *Fig. 1,is .alateral extension 104'which-controls the passage 70 and projectingto the right of the lower end of arm 100 is a lateral extension 106which controls the passage 80. Normally, at low temperatures, before theengine is started, the parts are in the position shown in Fig. 3, theextension 104 is in registry with the upper end of passage 70 andsubstantially blocks the how of air from said passage into the chamberA, while the extension 106 is in such a position that the upper end ofpassage 80 is open and air can flow freely from such passage into thechamber B. With the parts in the position described, the choke valve isclosed. Air flowing into the chamber B will flow directly into thesuction and on into the carburetor without passing through chamber A,but when passage 70 is open and heated air is admitted to chamber A, itflows through such chamber, heating the thermostat directly, passesthrough the opening in partition plate 42 into chamber B and then intothe suction passage.

When the engine starts to run under its own power there is, as hasalready been set forth, a very considerable increase in engine suctioneffective on the piston and also some increase in that directlyeffective on the unbalanced choke valve. This increase in suction movesthe piston 50 to the left, as seen in Fig. 2 and, depending on operatingconditions and temperatures, to a position where the forces exerted bysuction are balanced by the opposing force exerted by the thermostat.This movement of the piston, of course, effects a movement of the chokevalve toward open position, but at low temperatures this initialmovement of the valve is not very great. Then, as the temperature of theengine increases, during the warm-up period, the force exerted by thethermostat progressively decreases and the choke valve progressivelyopens. As already pointed out, this opening of the choke valve occurstoo rapidly in some installations if heated air from an exhaust stove isdrawn directly past the thermostat, when the application of heat to theintake manifold is insufficient to effect heating of the mixturesupplied to the engine in more or less accord with the heating of thethermostat. This results in too much opening of the choke valve andformation of too lean a mixture to effect satisfactory operation of theengine in such installations as are referred to.

In order to eliminate this difficulty, the member 104 is so arrangedthat it blocks the passage 70 when the choke valve is closed, as it isat low temperatures, but the member 106 is not in position to block thepassage 80 until the choke valve has made a very considerable movementtoward open position. When the passage 70 is closed and the passage 80is open, so that hot air is drawn through chamber B, there is someheating of the thermostat, so that its closing force is slowly reduced,but this is not effected nearly as rapidly as if the hot air was drawndirectly past the thermostat through the chamber A. The opening of thechoke valve is, therefore, delayed by blocking the passage 70, incomparison with a choke mechanism of conventional construction.

As the choke valve opens, the passage 70 is ultimately unblocked and asthis occurs, the member 106 is moved into position to block the passage80. The members 104 and 106 are of such magnitude that the passage 70 isnot opened, nor the passage 80 closed until the choke valve isapproximately 60 open. By the time the valve reaches this position inthis device when the heating of the thermostat is no longer retarded,the manifold is relatively hot and the piston 50 has moved to such aposition that there is but little suction effective on the piston.Because of these facts, the heating of the thermo- .statQshould be morerapid. so. that movement of the choke walve-during. the. last part ofthe opening. movement, i. e. from 60 .on, :will .be. rapid enough to,prevent the formatlOI1 0ff8.miXtu1'e that would -be too richforxmost-satisfactory operation. It is for this reason that the passage70 is unblocked when the valve gets 60 open and during further openingmovement the thermostat is heated much more rapidly and the choke valveis opened more rapidly.

During all operation after the temperature of the engine has risensufficiently to effect the unblocking of the passage 70, such passageremains open so that during all normal operation of the engine thethermostat is subject to the full heating effect of the hot air passingdirectly through the chamber A and the hot air is caused to pass throughchamber B only during a part of the warm-up period when the engine isstarted at relatively low temperatures.

While the form of embodiment of the invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted, as may come within the scope of the claims whichfollow.

What is claimed is as follows:

1. In a carburetor for use on an internal combustion engine and which isadapted to supply said engine with a combustible mixture of fuel andair, an air inlet passage for admitting air to said carburetor, a chokevalve in said passage controlling the passage of air therethrough, meansresponsive to temperature and suction for variably controlling theposition of said choke valve in accordance with variations in enginetemperature and suction, said means being effective to progressivelymove said choke valve toward open position as the engine temperatureincreases during the warm-up period following starting of the engine atrelatively low temperatures, a housing, a partition in said housingdividing such housing into two chambers in one of which said thermallyresponsive means is positioned, a conduit for conveying heated air toboth of said chambers, a passage communicating the engine suction tosaid chambers so as to cause a flow of heated air therethrough, valvemeans for controlling admission of air from said conduit tosaid chambersnormally positioned to prevent admission of air to the chamber in whichthe thermostat is positioned and to admit air to the other chamber whenthe temperature is low and the choke valve closed, and means for movingthe valve means to admit heated air to the first chamber and preventadmission of air to the second chamber as the choke valve is movedtoward open position upon increase of temperature.

2. In a carburetor for use on an internal combustion engine and which isadapted to supply said engine with a combustible mixture of fuel andair, an air inlet passage for admitting air to said carburetor, a chokevalve in said passage controlling the passage of air therethrough, meansresponsive to temperature and suction for variably controlling theposition of said choke valve in accordance with variations in enginetemperature and suction, said means being effective to progressivelymove said choke valve toward open position as the engine temperatureincreases during the warm-up period following starting of thte engine atrelatively low temperatures, a housing, a partition in said housingdividing such housing into two chambers in one of which said thermallyresponsive means is positioned, a conduit for conveying heated air toboth of said chambers, a passage communicating the engine suction tosaid chambers so as to cause a flow of heated air therethrough, valvemeans for controlling admission of air from said conduit to saidchambers normally positioned to prevent admission of "air to the chamberin which the thermostat is positioned and to admit air to the otherchamber when the temperature is low and the choke valve closed, andmeans operatively connecting said valve means to the choke valve wherebymovement of the choke valve toward open position upon increase oftemperature eflFects movement of said valve to a position to admitheated air to the first chamber and References Cited in the file of thispatent UNITED STATES PATENTS Coffey Dec. 6, 1938 Coffey July 27, 1943Olson Dec. 28, 1954

